The present invention relates to a method of removing a molten deposit mainly comprising oxides generated near a waste gas exit of a non-ferrous smelting furnace, and an apparatus therefor, particularly adapted for use in a copper flash-smelting furnace.
FIG. 8 illustrates a schematic construction of a copper flash-smelting furnace 100. The flash-smelting furnace 100 comprises a reaction shaft 101, a settler 102, and an uptake103. Copper concentrate in the form of a dried fine powder and an oxygen-enriched air or a high-temperature blast are blown at a time into the reaction shaft 101. The copper concentrate and the oxygen-enriched air or hot blast are instantaneously subjected to an oxidation reaction. The copper concentrate melts under the effect of the reaction heat thereof, and in the settler 102, is separated into a mate 104 containing about 60% Cu and a slag (not shown) having a Cu grade of under 1%. The mate is further refined in a converter and a subsequent process into blister copper. The slag is sent to an electric furnace annexed to the flash-smelting furnace, in which, after recovery of part of Cu contained in the slag, the slag is granulated by means of sea water, and used as a material for cement.
Waste gas from the flash-smelting furnace having a temperature of about 1,300.degree. C. and an SO.sub.2 concentration within a range of from 10 to 40% is fed from an exit opening 105 of the uptake 103 to a waste-heat boiler 200 to cool waste gas and the sensible heat is recovered in the form of a high-pressure steam. Then, after dust is removed by an electrostatic dust precipitator, waste gas is sent to a sulfuric acid plant to recover SO.sub.2 as sulfuric acid.
The flash-smelting furnace 100, in which oxidation reaction heat of concentrate can be effectively utilized, has a lower fuel consumption ratio as compared with the other processes, and permits supply of high-concentration SO.sub.2 to the sulfuric acid plant, resulting in such advantages as a high recovery ratio of SO.sub.2 and favorable merits in the aspect of environmental protection.
In the flash-smelting furnace, however, generation of peroxides is inevitable because fine powdery concentrate is oxidized during a very short residence time in the reaction shaft 101, and produced peroxides flow, as dust together with waste gas flow, from the settler 102 through the uptake 103 into the waste-heat boiler 200. Since peroxide have generally a high melting point, part thereof adheres to the settler 102 side walls or portions around the uptake 103 where temperature is relatively low as shown in FIG. 9, thus becoming a molten dust deposit commonly known as a wall accretion 106. If left unremoved, this molten dust deposit gradually grows and causes a clogging trouble in the uptake 103. Because dust is in semi-molten state, the molten dust deposit may flow on the wall surface and drops into the settler 102, thus causing operational troubles such as reduction of the furnace volume and slag hole clogging.
With a view to removing this molten dust deposit 106 which mainly comprises magnetite (Fe.sub.3 O.sub.4), a high-grade Fe oxide, the present inventors found it effective to achieve a low-melting-point slag by the addition of a reducing agent, and developed a method of preventing molten dust deposit from growing by injecting granular coke as a reducing agent into the uptake section 103 by pneumatic transportation, and bringing the same into contact with the molten dust deposit on a waste gas flow. This method has already been in actual use (Japanese Patent Application Laid-Open No. H01-87,728).
The granular coke blowing apparatus now in use is however dependent upon dispersion of a reducing agent (glanular coke) by waste gas flow in the furnace and contact thereof with molten dust deposit, and it is difficult to spray coke serving as the reducing agent over a wide range and certainly to a growing portion of the molten dust deposit. It is therefore impossible to prevent local growth of the molten dust deposit at the uptake ceiling or the top side wall, failing to achieve a complete resolution of the problems.
The present invention has therefore an object to provide a method and an apparatus for removing furnace deposit of a non-ferrous smelting furnace, which permits effective removal of a molten dust deposit over a wide range for an overall growing portion of molten dust deposit.